1. Field of the Invention
The present invention relates to a method of processing a substrate, such as a semiconductor wafer or a glass plate for an LCD, and a processing apparatus for carrying out the same.
2. Description of the Related Art
Generally, a semiconductor device fabricating process uses a cleaning system for clearing a surface of, for example, a semiconductor wafer (hereinafter referred to simply as xe2x80x9cwaferxe2x80x9d) of contaminants, such as particles, organic contaminants and metallic impurities, adhering to the surface. Usually, a single-wafer cleaning system is provided with a spin processor.
This prior art processor carries out a xe2x80x98scrub cleaning processxe2x80x99 to remove effectively particles adhering to the surface of a wafer. The scrub cleaning process brings a rotating end effector provided on its lower surface with a brush or a sponge pad into contact with a surface of a wafer held by a spin chuck to scrub off particles and the like adhering to the surface of the wafer. The processor has an arm capable of vertical movement and turning, and an air cylinder actuator held on the free end of the arm. A spindle capable of vertical movement and rotation is disposed below the air cylinder actuator, and the end effector is attached to the lower end of the spindle.
The air cylinder actuator exerts a vertical thrust through the spindle to the end effector to press the end effector against the surface of the wafer. A contact pressure (force exerted per unit area) actually applied to the surface of the wafer by the end effector is equal to the sum of the thrust exerted on the end effector and the weight of the end effector. If an excessively high thrust is applied to the spindle and the contact pressure exceeds a permissible limit, the surface of the wafer will be damaged. The arm is provided with a weight sensor capable of sensing the thrust acting on the spindle to avoid damaging the surface of the wafer. The vertical actuating operation of the air cylinder actuator is controlled automatically on the basis of data obtained by the weight sensor in order that the contact pressure applied to the wafer by the end effector may be controlled through the regulation of the thrust acting on the spindle.
Although the weight sensor employed in the prior art processor is able to sense the thrust acting on the spindle, the same is unable to measure the contact pressure of the end effector directly. Therefore, the weight sensor is incapable of sensing the variation of the contact pressure actually applied to the surface of the wafer by the end effector with respect to a predetermined contact pressure due to disturbances affecting the spindle, such as the frictional resistance of a bearing and torque for rotating the spindle.
A prior art processor disclosed in JP-A No. 8-267023 holds a wafer by a spin chuck formed by detachably attaching a mount to a rotating shaft. When measuring a contact pressure actually applied to the surface of the wafer, the mount is replaced with a sensor for sensing the contact pressure applied by an end effector. The contact pressure applied by the end effector to the wafer W can be measured by bringing the end effector into contact with the sensor in a manner in which the end effector is brought into contact with the surface of the wafer W.
The prior art processor disclosed in JP-A No. 8-267023, however, needs to attach the sensor to the rotating shaft to measure the contact pressure applied by the end effector. For example, when successively cleaning twenty-five wafers one at a time, it is impossible to ascertain, while the wafers are in process, that the contact pressure applied actually to the surfaces of the wafers is truly in coincidence with the predetermined level. If it is desired to measure the contact pressure, the cleaning process needs to be interrupted, which reduces the throughput of the cleaning process. Work for attaching the sensor to the rotating shaft requires additional time.
Rise in the level of integration of semiconductor devices requires the enhancement of the precision of contact pressure control. However, the prior art processor has difficulty in precisely controlling the contact pressure applied by the end effector through the measurement of the contact pressure during a cleaning process and the adjustment of the thrust acting on the spindle on the basis of measured data. It is possible such incapability of the processor reduces the reliability of the cleaning process.
The prior art processor has the arm capable of vertical movement and turning, the spindle capable of vertical movement and rotation and supported on the free end of the arm, and the end effector attached to the lower end of the spindle. The arm is turned and moved several times (at least twice) at least from the center of the wafer to the circumferential edge of the same to clean the surface of the wafer uniformly. Since the prior art processor uses only the single end effector throughout the cleaning process, it is possible that particles adhered to the end effector in an initial stage of the cleaning process, i.e., in a precleaning stage in which the surface of the wafer is cleaned with water, are transferred and adhere again to the surface of the wafer in a final stage of the cleaning process, i.e., in a finish cleaning stage, to reduce the cleaning effect of the cleaning process.
It is preferable, in view of satisfactorily achieving the cleaning process, to use an end effector provided with a cleaning member, such as a brush, suitable for cleaning the surface of the wafer provided with a film, such as an oxide film, a polysilicon film, an aluminum film or a nitride film. Since only the single end effector is supported on the arm, the processor is able to clean satisfactorily the surfaces of wafers provided with only limited kinds of films. Accordingly, a plurality of processors are needed for carrying out different cleaning processes for cleaning wafers respectively provided with different kinds of films.
Furthermore, the end effector detachably attached to the spindle needs to be replaced with a new one when the functional property of the end effector is changed, the end effector is deformed or the density of the working surface of the end effector is made irregular by the repetitive use of the end effector for the cleaning process. Replacing the worn end effector with a new one needs manual work, takes time and increases maintenance work.
Accordingly, it is an object of the present invention to provide a processing apparatus and a processing method capable of properly and easily obtaining accurate data on the contact pressure applied by an end effector to a workpiece while a process is being carried out.
Another object of the present invention is to provide a processing apparatus and a processing method capable of readily changing an end effector so as to meet the purpose of a process, use and the number of cycles.
With the foregoing object in view, according to a first aspect of the present invention, a processing apparatus comprises a holding means for holding a substrate, an end effector to be brought into contact with a surface of the substrate held by the holding means and capable of being retracted to a waiting position away from the surface of the substrate, and a measuring means for measuring contact pressure applied by the retracted end effector in the waiting position.
When successively processing a plurality of substrates by the processing apparatus in the first aspect of the present invention, the end effector is retracted to the waiting position after the completion of one cycle of a process for processing a substrate. Then, the measuring means measures directly the contact pressure applied by the end effector to see whether or not a normal contact pressure is applied to the surface of the substrate. If the measured result indicates that the normal contact pressure is applied to the substrate, the next substrate is processed. The process is continued until an abnormal contact pressure outside a permissible range of contact pressure is detected. Since the contact pressure can properly be measured, the process is not interrupted. The contact pressure may automatically be adjusted to the predetermined contact pressure when the deviation of the contact pressure from the predetermined contact pressure is detected by measurement, the contact pressure may automatically be adjusted to the predetermined contact pressure. Since the measuring means is disposed beforehand at a position near the waiting position, any preparatory work for measurement is unnecessary and the contact pressure can simply be measured.
Preferably, the measuring means of the processing apparatus in the first aspect of the present invention comprises a table on which the end effector is placed, and a measuring mechanism capable of sensing and measuring a contact pressure applied to the table to determine a contact pressure applied by the end effector. The end effector is mounted on the table and a contact pressure applied to the table by the end effector is measured by the measuring mechanism. The contact pressure applied to the table can be considered to be equal to that applied to the substrate by the end effector.
Preferably, the table is disposed with its support surface on the level of the surface of the substrate held by the holding means. Thus the table is disposed with its support surface on the level of the surface of the substrate held by the holding means and the support surface of the table can be regarded as a substitute for the surface of the substrate. The condition of the end effector pressed against the table is equivalent to that of the same pressed against the surface of the substrate during the process. Therefore, the contact pressure need not directly be measured during the process and the contact pressure applied to the substrate during the process can accurately be estimated from the contact pressure measured with the end effector pressed against the table.
Preferably, the end effector is placed on a table, and a processing liquid supplying means supplies a processing liquid over the substrate held by the holding means, and the measuring means is provided with a processing liquid supplying mechanism for supplying the processing liquid. The processing liquid supplying means supplies the processing liquid to the substrate during the process to enhance the effect of the process. During the measurement of the contact pressure, the processing liquid supplying mechanism supplies pure water to serve as a substitute for the processing liquid supplying means. Thus, data accurately corresponding to the contact pressure applied to the substrate during the process can be obtained. If the processing liquid is pure water, it is desirable to supply the processing liquid over the end effector during the measurement to clean the end effector.
Preferably, a cleaning means for cleaning the end effector is disposed at the waiting position, and the cleaning means comprises a supporting member for supporting the end effector thereon and a cleaning liquid supplying mechanism for supplying a cleaning liquid. The end effector can be cleaned by the cleaning means. Preferably, the cleaning means and the measuring means are disposed close to each other. When the cleaning means and the measuring means are thus disposed, transition from a measuring operation for measuring the contact pressure to a cleaning operation for cleaning the end effector can quickly be achieved.
The processing apparatus may further comprise an end effector support member for supporting the end effector, and a plurality of spare end effectors capable of being supported on the end effector support member may be kept in reserve. The end effector supported on the end effector support member is used for processing the surface of a substrate, and the end effector is replaced with selected one of the spare end effectors according to the purpose and use of the process or after the end effector has been used for a predetermined number of cycles of the process. The selected end effector is attached to the end effector support member for the subsequent cycle of the process.
Preferably, the processing apparatus is provided with first and second end effectors, and the first and the second end effector are attached alternately to the end effector support member. When processing a substrate, the first end effector is attached to the end effector support member to use the same for a first process, such as a preprocess, and then the first end effector is replaced with the second end effector to use the second end effector for a second process, such as a finishing process. Therefore, particles adhered to the first end effector during the first process are not carried over to the second process. The uncontaminated second end effector is used for processing the surface of the substrate by the second process. The use of the first and the second end effector for the first and the second process, respectively, prevents the redeposition of the particles removed by the first process on the substrate during the second process, which enhances processing effects.
According to a second aspect of the present invention, a processing apparatus for processing substrates comprises a substrate holding means for holding a substrate, end effectors to be brought into contact with the surface of the substrate held by the substrate holding means to process the surface of the substrate, and an end effector shifting means for shifting each of the end effectors between an end effector changing position where the end effector is replaced with another end effector and an end effector keeping position where the end effector is kept; wherein the plurality end effectors are kept in reserve, and desired one of the plurality of end effectors is attached to the end effector support member.
When the processing apparatus according to the second aspect of the present invention changes the end effector, the end effector support member is moved to the end effector changing position, the end effector is removed from the end effector support member, and the end effector is transferred to the end effector shifting means. The end effector shifting means shifts the end effector removed from the end effector support member from the end effector changing position to the end effector keeping position, shifts selected one of the end effectors from the end effector keeping position to the end effector changing position. The end effector support member is moved to the end effector changing position, the selected end effector is attached to the end effector support member to complete an end effector changing operation.
An end effector shifting arrangement will concretely be described. Preferably, the end effector shifting means includes a turning table provided thereon with a plurality of support vessels for supporting the end effectors thereon. The end effector shifting means may be provided with a cleaning liquid supplying mechanism to supply a cleaning liquid over the end effector to clean the same.
Preferably, the end effector support member is an arm, a spindle is supported for rotation and vertical movement on the arm, and the end effector can detachably attached to the lower end of the spindle so that the end effector can be replaced with another one. Thus, the end effector can easily be attached to and removed from the arm.
Preferably, the spindle is provided its lower end part with a hooking part, and the end effector is provided with a retaining part with which the hooking part is engaged. The hooking part of the spindle is engaged firmly with the retaining part of the end effector to connect the end effector to the spindle so that the end effector may not fall of f the spindle during the process. When replacing the end effector with another one, the hook part is disengaged from the retaining part, the end effector is removed from the spindle, and then the hook is engaged with the retaining part of another end effector.
The end effector may be provided on its upper part with a projection, and the spindle may be provided on its lower end part with a chucking mechanism capable of gripping the projection. This arrangement, similarly to that mentioned in claim 7, enables the arm to achieve work for removing the end effector from and attaching the end effector to the spindle.
According to a third aspect of the present invention, a processing method, which process a surface of a substrate held by a holding means by bringing an end effector into contact with the surface of the substrate, moves the end effector away from a position above the substrate and measures contact pressure to be applied by the end effector to the substrate during a process for processing the substrate and/or during a period in which the substrate held by the holding means is removed from the holding means and carried away, and another substrate is held by the holding means for processing.
This processing method is able to measure the contact pressure, for example, while a plurality of substrates are being processed successively without interrupting a processing operation for successively processing the substrates.
Preferably, the end effector is moved away from the position above the substrate and cleaned during a process for processing the substrate and/or during a period in which the substrate held by the holding means is removed from the holding means and carried away, and another substrate is held by the holding means for processing. Thus, the end effector can be cleaned without interrupting a processing operation for successively processing the substrates.
Preferably, a plurality end effectors are kept in reserve, and the end effector is changed periodically. Thus, the end effector is replaced with another one after processing one or a plurality of substrates. End effector changing time may optionally be determined so as to meet the purpose of the process, use and the number of cycles. For example, in a process for processing one substrate, the end effector may be changed for each of a first stage for a preprocess, a second stage for an intermediate process, a third stage for a second intermediate process, and a fourth stage for a finishing process. The end effector may be changed when the end effector is deformed, after the end effector has been used for a predetermined time for processing or after the end effector has been used for processing a predetermined number of substrates. For example, an end effector or a set of end effectors is used continuously, the end effector or the set of end effectors is replaced with another end effector or another set of end effectors when the former is deformed, the end effectors are subjected to maintenance work after all the available end effectors have been deformed. The plurality end effectors are removed and a plurality of new end effectors are kept in reserve. The prior art processing method uses only one end effector and needs to carry out maintenance work every time the end effector deteriorates. The processing method of the present invention extends a maintenance period and reduces time necessary for maintenance work.
Preferably, the processing method keeps a plurality of end effectors of different types in reserve to use those end effectors selectively for surface processing according to the surface condition of the substrate. Thus, the end effectors of different types suitable for processing films of different kinds formed on the surfaces of substrates are used selectively. Accordingly, one processing system can be used for processing substrates provided with different kinds of films, respectively, and footprint can be saved.
Preferably, first and second end effectors are kept in reserve, the first end effector is used for processing a substrate by a first process, and the second end effector is used for processing the same substrate by a second process.